VIEWPOINT: Dams without beavers: could beaver dam analogues yield benefits in the UK?BDAs are simple and cheap to construct. Here, a row of wooden posts is being inserted into the bed of thecreek in order to secure the BDA. USFWS Pacific Southwest RegionThe streams were no longer connected to thefloodplain, and the fertile valley bottoms driedout. In the USA, therefore, the role of beaversin the creation of complex fluvial systemswas obvious, leading to recognition of streamevolution as an eco-geomorphic process; one thatis not only influenced by physical features, suchas gradient and flow, but also by living organisms,such as beavers and plants.BDAs in the USAIn the 1970s and 1980s, the restoration of riversystems in the USA was deemed necessary in orderto reverse declines in salmonid populations, whichled to the idea of imitating the actions of beavers inplaces where they were scarce or absent, or wherecreeks were so heavily degraded that reintroductionof the animals was not an option. As a result, theecologist Michael Pollock developed the concept ofand construction methods for BDAs, and pioneeredtheir use as a cheap, relatively simple technique(Pollock et al. 2015).The BDA movement began in Bridge Creek,Oregon, in 2007, when Pollock and his colleaguesattempted to strengthen existing beaver damswith wooden posts in order to prolong their lives.Subsequent work revealed a positive correlationbetween salmon populations and the presence ofthese dams, which led to the initiation of a moreambitious programme of building structuresthat imitated beaver dams along a 3.4km stretchof Bridge Creek (Pollock et al. 2014). Initially76 BDAs were constructed, with a further 45added between 2010 and 2012. In the four yearsafter BDAs were first installed, the production(population density, growth and survival) ofyoung steelhead salmon rose by approximately175% (Bouwes et al. 2016).Following the success of the Bridge Creek trial,BDAs have become probably the most widespreadtool in the restoration of river systems throughoutthe USA. BDAs offer a number of advantagesover other hard-engineering options: they aresimple and cheap to construct, ideally suited tobeing built by volunteer labour; they use materialsthat are readily available on site; and they aregenerally free of bureaucratic constraints, such asplanning regulations, because they are essentiallyConservation Land Management Summer 2022 | Vol. 20 No. 2 31
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